This invention relates to the handling of RF signals. In particular, this invention is a complex weighter for providing an RF signal with controlled phase shift and amplitude.
Many electrical systems that process RF signals require a signal that is synchronized with another RF signal but that differs from it controllably in amplitude, phase, or both. The differences in amplitude and phase may be fixed or they may vary in response to a control signal. An example of such a system is a single-frequency repeater with adaptive cancellation. A major problem in such a system is to separate a received portion of a retransmitted wave (the so-called "blowover" signal) from the much weaker received signal that is to be rebroadcast. One way of neutralizing the effect of such a blowover signal is adaptive cancellation in which a signal corresponding in frequency, amplitude and phase to the output signal is subtracted from the input to leave only a desired received signal. The signal to be subtracted is readily derived from the transmitted signal but, in general, differs from that signal in both amplitude and phase.
Other systems that require synchronized signals differing in amplitude or phase from a reference signal include side-lobe cancellers and sideband noise cancellers. A side-lobe canceller is a receiving system for directing a null in an antenna pattern at a jamming signal. The null is produced by pointing a second directive antenna at the jammer and adjusting its receiving amplitude to be equal to that of the first antenna, but out of phase so as to cancel in a passive summing network. A sideband noise canceller is a system for cancelling an unwanted signal by subtraction.
Various measures of control of RF signals to frequency ranges as high as one gigahertz have been achieved with combinations of microwave couplers and PIN diodes. In some of these applications, the PIN diodes have been biased to appear either as short circuits or as open circuits to terminate portions of couplers with reflection coefficients of +1 or -1. The result is to make microwave switches that are controlled by external DC sources. None of these applications provides continuous control of amplitude or phase of an RF signal over a range.
It is an object of the present invention to provide a controller for RF signals that produces an externally controllable phase shift.
It is a further object of the present invention to provide a circuit for controlling externally the amplitude of an RF signal.
It is a further object of the present invention to provide a circuit to control both amplitude and phase of an RF signal.
It is a further object of the present invention to perform complex weighting with a minimum number of components.
Other objects will become apparent in the course of a detailed description of the invention.